A tape cartridge for a magnetic instrument is required to be loaded by inserting the tape cartridge into a holder. In such an apparatus for loading the tape cartridge, the holder holding the tape cartridge is required to be locked to a cartridge operative position when it is brought from a cartridge loading/unloading position to the cartridge operative position.
However, in such a prior apparatus, the holder is locked to the cartridge operative position even when the tape cartridge is not inserted into the holder. Thus, if the apparatus is provided with a plunger to relieve locking of the holder, there is required the unloading operation of the plunger to relieve the locking of the holder by electrically exciting the plunger. Furthermore, another tape cartridge tends to be erroneously inserted into the holder in spite of the tape cartridge already held by the holder.